Mass spectrometer control



s. B.. s'PRcKLEN g/Powerfzfppiy 3.] /l .fec'orzer I IN VEN TUR. fanjford Jpracie Patented June 2, 1953 MASS SPECTROMETER CONTROL Stanford B. Spracklen, Oak Ridge, Tenn., assignor to the United States of America as represented by the United States Atomic Energy Commission Application February 21, 1946, Serial No. 649,414

(Cl. Z50-41.9)

3 Claims.

This invention is concerned with mass spectrometers and their operation and provides improvements to the end that proper sensitivity is maintained by insuring against operation above an established critical pressure, and protection is provided for the elements within the mass spectrometer against excessive pressure increases.

As is known, a mass spectrometer is an apparatus for sorting ions which have different massto-charge ratios and therefore different specific masses, and is normally used for the qualitative or quantitative analysis of elements contained in mixtures, compounds, mixtures of compounds, or for the determination of the isotopic ratios which exist within most elements.

Protective devices found on mass spectrometers are normally designed to serve the purpose of protecting` the mass spectrometer elements in the usual laboratory use of such instruments. When mass spectrometers are used in production control analysis, it is found that the normal protection devices are not adequate for such production control. The inadequacy results from the fact that the design of the protective devices is based entirely upon the critical pressures which may cause injury to the elements of the mass spectrometer and the associated pressure gauge, and not upon the pressure range at which the mass spectrometers should be operated to obtain a desired sensitivity. In production control analysis it is of major importance to maintain a relatively constant sensitivity so as to facilitate the interpretation of control analysis results. This relatively constant sensitivity can only be maintained if the mass spectrometer is operated below a predetermined pressure. The control circuit of the invention prevents operation at pressures higher than the predetermined pressure until a manual reset of sensitivity has been made by the operator and in addition provides protection against improper energization of the elements within a mass spectrometer. Such a manual reset is particularly desirable when production analysis makes it expedient to operate delicate instruments, such as mass spectrometers, with personnel who may not be particularly technically qualified to understand the operating characteristics of such instruments.

An object of my invention is to provide a means for maintaining a relatively constant sensitivity in a mass spectrometer by preventing operation above a predetermined pressure.

Another object of my invention is to provide an automatic lock-out, which, when the pressure exceeds the predetermined pressure, will prevent further mass spectrometer operation.

Still another object of my invention is to provide a manual reset of the automatic lock-out which is ineffective when the automatic lock outis set to respond to changes from thedet sired sensitivity range, but which is effective when set to respond to changes from higher pressure ranges.

These and other objects of my invention will be understood more thoroughly from the following description when read in conjunction with the accompanying drawing, the single gure of which is a schematic diagram of a control arrangement incorporating my invention.

With reference to the drawing, the mass spectrometer shown generally includes an ionization chamber 25, a high voltage accelerating electrode 26, an analyzing chamber 21, and an ion collector plate 28, used in conjunction with an ionization pressure gauge 2li, all disposed within an envelope 29'which is highly evacuated by an associated high vacuum system, not shown. The current produced on the collector plate 28 is normally amplified by a direct current amplifier Si), whose output is recorded either visually or graphicallyT by a suitable metering device 3I. The ionization gauge 24 has an associated circuit 32 which provides power and indicates pressure. The mass spectrometer is provided power for the high voltage and iilament circuits through a regulated power supply 34.

The control arrangement shown in the draw ing comprises a gaseous discharge tube I2, such as a thyratron tube, having its control grid I I connected by a lead I3 so as to be iniiuenced by the voltage drop across a resistor Ill developed by a pressure representative current from an ion gauge 24. Voltage is applied to the plate 35 of the tube I2 through a first relay coil I'I and a contact switch 22. The pressure range response of the tube I2 is controlled by a two position double pole switch I5. When the switch I5 is in the 10-6 mm. pressure range position, one pole completes a circuit around the contact switch 22, thus providing another path through which the voltage is impressed upon the plate 35 of the tube I2 through the relay coil I1. The relay coil I1 has its armature 36 connected in series relationship with the primary I8 of an ion gauge transformer 33 between external 110 volt power lines I6. Thearmature 36 is also connected in series relationship with a second relay coil I9 Yand a third relay coil 2U having armatures ,3.1 and 38, respectively, and a contact switch 23 between external 110 volt power lines I6. This arrangement rmakes it possible to energize the ion gauge primary I8 either independently of or simultaneously with the relay coils I9 and 20 by the action of the opening or closing, respectively, of the contact switch 23. The contact switches 22 and 23 are arranged to be actuated simultaneously by a push button 2I. The purpose of this arrangement is to make it possible to operate an ion gauge filament 4I,

which is .series connected to the secondary winding 39 of the ion gauge transformer 33, either independently of or simultaneously with a mass spectrometer filament 4U, which is series connected to the armature 31 of the relay coil I9 and a D. C. power supply 34, and the high voltage accelerating electrode 26, which .is series connected to the armature 38 of the relay coil 2U and the D. C. power supply 34.

The relay coil il' may also be energized by means of a single pole single throw switch I4 through the contact switch 22 to a voltage source B+. This arrangement makes it possible to prevent the armature 38 operated by relay coil I1 from energizing .the circuits connected in series with its armature 35 dining the startup period 'when the pressure within the mass spectrometer is too great to safely energize the ion gage filament 4I.

In the operation of the above described arrangement, the from the ionizaton giu '.212 is transmitted through the resistor ID to the ionization gauge ampliiier 32, well known manner. The signal voitage produced across the resistor I6 is representative of the pressure within the ionization gauge 24, and therefore of sure within the connecting nine" spectrometerl envelope 29. The signal voltage across the resistor I increases in posfive polarity with an increase in pressure within the en- 29 and conversely a decrease in positive s "ts from a decrease in pressure. A portion of this signal voltage is upon the `grid il of the thyratron tube i2 through the lead I2. The ionization gauge 24, ionization gauge transformer 33, resistor lil, the ionization amplifier and power supply are all parts oi a conventional ion-ization gauge power source and amplifier system, and are not claimed part of my invention.

"reccding the pumping-down of the mass spectrometer, the single pole single throw switch 'lf3 is closed and the ltwo position double pole in Athe i()-5 mrn. range "i'he closed switch lil -eiie zes the relay coil I?? causing its armature 3; to open the circuits connecting the relay coils i9 and 2li and the ionization gauge vtrai'isformer primary I8 between the lll) volt lines le, thus allowing the elay coils I8 and 20, and said transformer primary l@ to -rein'ain dei-energized. Since the relay coil IS is not 'energized it allows its armature 3'. to remain open thereby permitting the circuit between the 'mass spectrometer rainent iii? end the D. C. power supply 34 to remain deenergized, vwhile thedeenergized relay c il allows its armature Yto remain open, thereby permitting 'the circuit between the accele ating electrode 25 and the DIC. power supply 3d to remain cle-energized. De-energization of the ionization gauge transformer primary I- prevents the energization of the ionization gauge filament dl.

plate voltage is applica to the plate 35 oi the tliyratron ,tube I2 through the contact switch 22 and the relay coil I'I. The cathode voltage of the tube I2, when `'the two position double pole-switch I5 'is in the 10-5 mm. pressure range posi n. Iis adjusted so that as vlong as the pressure within the mass spectrometer envelope l29 'remains above ZXliV mm. o'f Hg, .the signal 'voltage inpressedon the grid VAI=I of the thyratron tube I2 through lead t3 `will :be of such Amagnitude :as :to cause .the .thyratron tube .I2 to liire should the ionization gauge '24 be placed .into operation. 'When :the pressure or' or) in the neighborhood of lll-5 nim. of Hg, as read by a supplementary McLeod gauge or Pirani gauge, not shown, which is used in conjunction with the vacuum system, the pressure can be determined more precisely using the ionization gauge 24 by pressing a push button 2l which opens the contact switches 22 and 23 simul taneously. Opening the contact switch 22 deenergizes the relay coil Il causing its armature 3G to close the circuit between the ionization gauge transformer primary I8 and the 110 volt power lines IS, thus energizing the ionization gauge nlament 4l attached thereto, thereby resulting in the operation of the ionization gauge 24. Opening the Contact svitch 23 prevents the circuit between the relay coils I9 and 20 and the volt power lines I5 from being closed by the action of the armature 35 when its relay coil Il is de-energized- Since the relay coils I9 and 23 are not energized, their respective armau tures 37 and 38 remain in the open position and the respective spectrometer -filament and push button 2l, through its action oi opening the contact switches 22 and 23 simultaneousy, the mass spectroniete operator to check the pressure reading, by means of the ionization 2li, several times before the `drop.; to the value of 2 l05 mm. cf Hg in order to determine if any vacuum difficulties are being encountered, and yet provi es protection ior the mass spectrometer elements. The closed switch 4 `vill again energize the relay ycoil I1 causing its armature 3G to open the circuits otif. thereto when the contact switch 22 is o as to -pos""lvely prevent the mass spectroni cf circuits from becoming energized at a pr ure which might prove detrimental to the elcznentseontained within the mass spectrometer. When the pi ssure 's approximately' lf nim. .ol g as determined by the ionization gauge 2li, the single pole throw switch It opened. The grid II will control the operation of the thyratron tube I2 when the contact .switch Z2 is closed by the releasing of the 'push button :E It isto be noted that, as previously explained, the releasing of 'the push button y2l closes both of the kcontact switches 22 and 123 simultaneously. If .the `pressure in the mass spectrometer is 2` l`0-5 min. of Hg, or lower, the signal voltage produced -at the resistor I0 will be such that it will not cause the thyratron tube I2 to fire, and the coil Il will then remain deener gized and its armature 36 will remain closed, thereby :maintaining the energization ol the circuits attached thereto; suoli circuits being those .connecting the relay coils I!! and 20, and the ionization gauge transformer 4primary I8 between .the -Illl volt power lines l5. mergizing therelay coil III causes its armature l31 to close the crcuit between the D. C. power supply 34 and the mass .spectrometer iilament V4l), and energizing the relay coil 20 causes its armature 33 to .close the high voltage circuit between the D. C. `power supply `34 and the accelerating electrode 25. The ionization gauge transformer primary IS energizes the circuitvcontaining the ion gauge filament 4I, as previously'explained lIn the :event that an increase in pressure is experienced which is greater than the value of 2 .lO-5 mm. of Hg, the `thyratrontube I2 will fire and energize relay coil I1 thereby causing its armature 13G to open the circuit to the relay coils :I9 and '20, `and the ionization ygauge .trans- De-energizing the relay coils Si! it causes their .enectivs armatures il and to open circi ts attached thereto, which protects the spectrometer nlcinent FQ and the acceleratino electrode frein injury due to excessive ,re within the envelope Removal of the high voltage potential from the accelerating electrode 2S also provides protection for the D. C. power supply against excessive dr .s which develop during periods of excessive pressure within the envelope 2i?. When the pressure ywithin the envelope 29 has again been reduced to 2 lil5 of Hg, or lower, the spectrometer may be placed into operation by pressing the push button 2i which removes the plate voltage from the tube thereby deionizing it.

When pressure in the envelope has been reduced to a value of 2 lil-6 nim. of l-l'g, or less, as indicated by the ionization gauge 2li, such pressure being the me allowable value for a desired mass spectrometer sensitivity as required for normal operation, the two position double pole switch` is then placed in the lil*6 mm. pressure range position. The mass spectrometer is now ready for normal operation by the operational crew, With the switch l the 6 mm, pressure range position, the lock-out feature of the control circuit becomes effective when the pressure in the envelope 2.5i increases above the value of 2 lil-6 mm. of lrle. The loci;- out feature results from the iact that the plate 35 of the thyratron tube l2 receives its plate potential by parallel paths, one suc-h path connecting the plate through the relay coil il and the upper pole of the switch i5 to the supply voltage while the other path connects the plate 35 through the coil il and the contact switch 22 to the supply voltage. Now if the pressure in the envelope lill rises above the set value of 2 lil-6 of Hg, the thyratron tube l2 will fire and energize the relay coil il thereby causing its armature to open the circuits attached thereto, such circuits causing the opening of additional circuits connecting the mass spectrometer filament il and the accelerating electrode ZS to the mass spectrometer D. C. power supply 34 in the manner previously explained. Due to the lock-out feature, the operator cannot rese the control circuit and place the mass spectrometer in operation in the desired pressure range oi i0-s nun. or l-ilg by pressing the push button 2l to de-ionize the thyratron tube l?! as long as the two position double pole switch i5 is in the lil-6 min. pressure range position, because the contact switch 22 of the push button 2i is bypassed by the upper pole of the double pole switch l5 and therefore the plate potential of the thyratron tube Eil is maintained and the relay coil Il remains energized until 'the double pole switch 5 is changed from the lil-6 mrc. pressure range position.

It will be obvious to those skilled in the art that various changes may be made in this apparatus without departing from the spirit of the invention, and therefore the invention herein described is not limited to what is shown in the drawing and described in the specification, but only as indicated by the appended claims.

I claim:

1. In mass spectrometer operating means, an envelope enclosing spectrometer elements and an ionization pressure gauge, means for supplying foriner pri.

electrical energy to the spectrometer elements, means for energizing the pressure gauge, a gaseous discharge tube having at least a cathode, an anode and a control grid, means for impressing on the control grid a voltage corresponding to the pressure to whic said gauge is subjected, switch means for selectively impressin upon the cathode two different biasing voltages of such values with respect to the control grid that the voltages required on the control grid to fire the tube correspond, respectively, to a pressure at which the elements of the spectrometer may safely be energized and to a lower pressure below which consistent operation of Athe spectrometer at 'the desired spectrometer sensitivity can be had, and a normally closed switch in the anode circuit or" the tube and in parallel with said switch means when said switch means is in the position for consistent operation, whereby upon a pressure rise causing the tube to fire said switch means must be moved from consistent operation position in order to deionize the tube.

2. An analyzer system of the character deoribed comprising a mass spectrometer, circuits for energizing said spectrometer, a control circuit responsive to pressures within the spectrometer above a predetermined magnitude for opening the energizing circuits and denergizing the spectrometer, manually operated means for interrupting the control circuit to energize the spectrometer, and means coupled in parallel with manually operable means including a switch and circuit for altering the range of operation of control circuit, said last means being connected to by-pass and serve as a lock-out for manually operated means in response to the actuation of said switch to prevent interruption of the control circuit for a selected pressure range.

3. A system for the control of the energization of electrical elements in a mass spectrometer comprising an ionization pressure gauge in communication with the mass spectrometer, a source coupled to said pressure gauge for energizing it, a circuit for energizing the electrical elements of 'the mass spectrometer, means responsive to a predetermined pressure in said spectrometer for opening said circuit and maintaining it open, said last means including a gaseous discharge tube coupled to said pressure gauge and nred by signals therefrom at the predetermined pressure, and a relay in the output circuit of said tube and responsive to operation thereof for opening the energizing circuit to the mass spectrometer elements, means including a switch in the anode circuit of said tube for disabling it, and a lock in circuit including a second switch connected in parallel with said disabling means for maintaining the anode circuit and sustaining the operation of said tube.

STANFORD B. SPRACKLEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,783,234 Firestone Dec. 2, 1930 2,374,205 Hoskins Apr. 24, 1945 OTHER REFERENCES Henney: Electron Tubes in Industry, McGraw -Iill, i934, p. 180. (Copy in Div. 52.) 

